The present invention concerns the light measuring circuits for electronic computer flash apparatus. In particular it concerns such electronic computer flash apparatus wherein a photosensor receives light reflected by the object to be photographed and wherein the current created in the photosensor is applied to a resistor-capacitor integrator circuit whose output, in turn, is applied to the control electrode of a thyristor which initiates the termination of said flash.
In computer flash apparatus of the above described type, difficulties occur when the object to be photographed is very close to the flash because the action of the circuit in terminating the flash is not sufficiently rapid after a predetermined quantity of light, as determined by the voltage across the capacitor, has been received by the photosensor. For example the thyristors which control the flash termination have a finite operating time and, of course, at least some short delays are introduced by the various other circuit elements connected between the above mentioned thyristor which initiates the termination and the further switching element connected either in series or in parallel with the flash tube whose operation actually terminates the flash. For the large quantities of light falling on a close object and the therefore very short required exposure times, these delays generally result in an overexposure.